Paganism wasn't seen as "outdated" at the time. Hellenic paganism was the religion of most members of the Roman Empire (with regional variation). Judaism was the religion of a small ethnic minority, and only the main religion in one small area of the Empire. There were various revolts by the Jews against various Roman actions, particularly ones that the Jews felt violated their beliefs, which eventually led to the Romans destroying the Jewish temple in Jerusalem, and exiling Jews across the Empire. That was in 70AD.

Christians, however, were a bit different. Unlike Judaism, Christianity was a missionary religion that aimed to convert everyone, regardless of their ethnic background. It was started by Jews, but by 200AD most of its members were not Jews, but various other ethnic groups like Romans and Greeks.

Tldr; Judaism was only the majority religion in a small area, the area Christ came from, and didn't spread much. It didn't attempt much in the way of conversion, and its military/political power was smashed in 70AD. Christianity however, aimed to spread everywhere, replacing Roman Paganism through conversion. That's why many Romans disliked it.

They were murdered and spread over the roman empire in 70AD. Look up the Jewish Revolt on internet for further information. 130 years later the population was still low and there wasnt really a place where jews were concentrated.